AJP - Heart and Circulatory Physiology, Vol 249, Issue 3 505-H511, Copyright © 1985 by American Physiological Society
Dynamic interactions between heart rate and atrioventricular conduction
J. M. Loeb, J. M. deTarnowsky, M. R. Warner and C. C. Whitson
We examined the beat-by-beat alterations in atrioventricular (AV)
conduction time that accompany both linear and abrupt changes in heart rate
(HR). We used alpha-chloralose-anesthetized and autonomically decentralized
dogs (n = 10) and recorded electrocardiogram (ECG), arterial pressure, and
electrograms from sinus node, right ventricle, and His bundle. Abrupt or
linear HR changes of known slope were generated by computer and displayed
graphically with AV interval as a function of time. HR was increased
linearly from 10 to 110 beats/min above control over 15, 30, and 60 s and
then decreased in a linear fashion. AV interval was dependent on direction
of HR change with marked asymmetry between increases and decreases in HR.
Similar data were apparent irrespective of whether the decrease followed
the increase or vice versa. To study determinants of 1:1 conduction, HR was
increased linearly by 200 beats/min above control over 15, 30, and 60 s. As
rate of change of HR increased, 1:1 conduction continued to a higher HR;
however, the last conducted AV interval was negatively correlated with rate
of change of HR. Abrupt sustained increases in HR of 25, 50, 75, and 100%
above control resulted in marked accommodation of AV interval only at
higher levels of HR. Thus in the absence of autonomic neural tone, 1)
cardiac cycle length is not associated with a fixed AV interval but is
dependent on magnitude and direction of HR change; and 2) the HR at which
1:1 AV conduction fails is significantly altered by the rate of change of
HR.
